Laboratory Experiments No 4: Measurement and Estimation of the
Aerosol Light Scattering Coefficient
Purpose : To use an optical particle counter to determine the size-resolved number concentration, to use this information to estimate the light scattering coefficient (
 sp
), and to compare this estimate to
 sp
directly measured using an integrating nephelometer
Expt 1: Measuring and estimating
 sp
of monodisperse PSL of various concentrations

Setup instruments as shown in Figure 2

Put a filter upstream of the laminar flow element and measure the zero-air values for both the

OPC and nephelometer
Generate 0.7
 m PSL using the atomizer and stock solution (Note: In order to determine the actual concentration you will have to account for the dilution factor of the laminar flow element)

Record the OPC size distribution using the Labview program, and the nephelometer
 sp
from the panel of the instrumet

Estimate
 sp
from the OPC data and compare this value with the nephelometer measurement
Expt 2: Measuring and estimating
 sp
for polydisperse ammonium sulfate aerosol

Completely clean the atomizer and add ammonium sulfate solution

Generate ammonium sulfate aerosol

Measure the aerosol size distribution using the OPC and record the nephelometer
 sp
value
Suggested Laboratory analyses
 Present ‘zero air’ values for both the measured number concentration and scattering coefficient

Estimate the number concentration of PSL aerosol (using calibration curves obtained during laboratory 3) and use this value to estimate the scattering coefficient

Present and discuss the estimated versus measured light scattering coefficient for PSL

For ammonium sulfate plot both the mass and number size distributions

Use the ammonium sulfate size distribution to estimate the light scattering coefficient
Note: The above are minimum requirements for your analyses